Cruise control systems are designed to automatically control the speed of a vehicle. Specifically, when there are no leading vehicles, the cruise control system installed in a vehicle works to set the vehicle's speed to a desired constant speed determined by, for example, the driver.
When a leading vehicle is encountered, the cruise control system of the vehicle works to alter the vehicle speed to maintain a desired interval with respect to the leading vehicle while following the leading vehicle.
Some examples of such a cruise control system are disclosed in Japanese Patent Publication No. 2708751, Japanese Patent Application Publication No. H10-205366, and Japanese Patent Application Publication No. 2000-057498, which will be respectively referred to as “first patent publication”, “second patent publication”, and “third patent publication”, hereinafter.
In the first patent publication, a radar installed in a vehicle running along a lane of a road scans radio signals over a predetermined scanning field so as to detect an object that the running vehicle faces. A cruise control system installed in the vehicle obtains the speed of the vehicle detected by the radar.
When the detected speed of the object exceeds zero, the cruise control system determines the object as a leading vehicle running in the same direction as the vehicle to thereby capture it as a target for cruise control of the vehicle.
In contrast, when the detected speed of the object is equal to or lower than zero, the cruise control system determines that the object is a standstill or moving in a direction opposing the running direction of the vehicle to thereby discount the object as a target for cruise control of the vehicle.
In the second patent publication, a radar installed in a vehicle running along a first lane of a road scans radio signals over a predetermined scanning field so as to measure both a first distance and a first angle between the vehicle and a first leading vehicle running in the same first lane as the vehicle and both a second distance and a second angle between the vehicle and a second leading vehicle running in a second lane adjacent to the first lane.
A cruise control system installed in the vehicle obtains a first yaw relative velocity between the vehicle and the first leading vehicle based on the measured first distance and the measured first angle therebetween. Similarly, the cruise control system obtains a second yaw relative velocity between the vehicle and the second leading vehicle based on the measured second distance and the measured second angle therebetween.
Then, the cruise control system determines whether the second vehicle cuts in front of the vehicle from the second lane based on the measured first and second yaw relative velocities.
When it is determined that the second vehicle cuts in front of the vehicle from the second lane based on the first and second measured yaw relative velocities, the cruise control system alters the vehicle speed to maintain a desired interval with respect to the cut-in second vehicle while following the cut-in second vehicle.
In the third patent publication, a radar installed in a vehicle running along one lane of a road scans radio signals over a predetermined scanning field so as to measure a distance between the vehicle and forward vehicles that the vehicle face.
A cruise control system installed in the vehicle obtains an integrated count value that is counted up with increase in a shift length of each of the forward vehicles with respect to the lane marker of the one lane of the road.
When it is determined that the integrated count value of one of the forward vehicles exceeds a predetermined threshold value, the cruise control system selects the corresponding one of the forward vehicles as a track target of the vehicle.
When the radar-measured distance between one of the forward vehicles and the vehicle is comparatively low, a comparatively low value is used as the predetermined threshold value. In contrast, when the radar-measured distance between one of the forward vehicles and the vehicle is comparatively high, a comparatively high value is used as the predetermined threshold value.
In addition, when the shift length of one of the forward vehicles with respect to the lane marker of the one road is smaller than a normal shift length for track-target leading vehicles, in other words, the forward vehicle is assumed to travel close to the lane marker, a comparatively low value is used as the predetermined threshold value.
In contrast, when the shift length of one of the forward vehicles with respect to the lane marker of the one lane of the road is longer than the normal shift length for track-target leading vehicles, in other words, the leading vehicle is assumed to travel away from the lane marker, a comparatively high value is used as the predetermined threshold value.
For example, when another vehicle cuts closely in front of the vehicle from another lane adjacent to the one lane as a forward vehicle, the comparatively low value set as the predetermined threshold value allows the cruise control system to immediately select the forward vehicle as the track target of the vehicle. The cruise control system can therefore immediately grasp another vehicle that is cutting in front of the vehicle from another lane adjacent to the one lane.